The present invention discloses a method and a device for use in a wireless cellular access system in which users in a cell in the system receive transmission power control commands on a control channel.
In some cellular access systems, such as, for example, the Long Term Evolution (LTE) system, data in both uplink and downlink (i.e., from and to users, respectively) is transmitted on channels which are shared in both frequency and time between multiple users. Examples of shared so called physical channels in the LTE system are the Physical Downlink Shared Channel (PDSCH) and the Physical Uplink Shared Channel (PUSCH).
Due to the principle of shared channels, control signaling is necessary, at least in the downlink, i.e., to the users in the cells of an LTE system. One of the downlink control channels in the LTE system is the PDCCH channel, the Physical Downlink Control Channel. The PDCCH is used to carry Downlink Control Information, DCI, such as, for example, scheduling decisions, transmission power control commands, and other specific control signaling. In more detail, the downlink control information possible to send on the PDCCH includes:                Downlink scheduling assignments, including resource indications for the PDSCH transport format, hybrid-ARQ information, transport block size, MIMO-related control information if applicable, and Physical Uplink Control Channel (PUCCH) transmission power control commands.        Uplink scheduling grants, including resource indications for the PUSCH, the Physical Uplink Shared Channel, transport format, hybrid-ARQ related information, and PUSCH transmission power control commands.        Transmission power control commands of groups of user terminals as a complement to the transmission power control commands which are “piggy-backed” with the scheduling decisions.        
The PDCCH can use various formats for the DCI. However, regardless of the DCI format, the PDCCH will comprise a so called RNTI, Radio-Network Temporary Identifier, which is an identity for the user terminal for which the PDCCH and the associated DCI is intended. In order to enable the use of RNTI, each user terminal in a cell is assigned its own RNTI, the so called C-RNTI, which may be used when making downlink transmissions to that user terminal.
In each so called subframe, a user terminal monitors the PDCCHs in the cell. Upon detecting its own identity, the C-RNTI, in one of the PDCCHs, the user terminal declares the PDCCH contents valid, and follows the contents of the PDCCH. In the case of the PDCCH contents being downlink scheduling, the user terminal attempts to decode the associated data transmission on PDSCH resources pointed out by the PDCCH. The result of the decoding attempts, e.g., positive acknowledgement, ACK, or negative acknowledgement, NACK, is transmitted in uplink by the user terminal.
Based upon the ACK or NACK, a decision can be made on whether or not to transmit new data, i.e., when the ACK is received, or to retransmit the previous data, i.e., when the NACK is received, indicating that the user terminal's reception was in error. The ACK/NACK is usually transmitted on an uplink control channel known as the PUCCH, Physical Uplink Control Channel. As the reception of ACK/NACK is important for correct operation of the system, it is crucial to adjust the transmission output power of the PUCCH so that the received power is sufficiently high to correctly receive the ACK/NACK, but not so high that unnecessary interference is created in the system.
In order to control the PUCCH output power of user terminals in a cell, the PDCCH comprises two bits which signify the allowed transmission power of the PUCCH for a user terminal. The terminal uses the information given in these two bits to increase or decrease the PUCCH transmission power. In this way, the network can ensure that a proper level of transmission power is used by a terminal for the PUCCH.
The C-RNTI is, as mentioned above, the unique user terminal identity of the terminal for downlink addressing purposes. However, in addition to having a C-RNTI for the purposes of downlink “unicast” data, each terminal can also be allocated one or several so called “group RNTIs”. A group RNTI is an identity which is common to a plurality of terminals in a cell, and is consequently used to transmit downlink information which is relevant to more than one terminal.
One example of such information is system parameters which are necessary for all the terminals in a cell in order to be able to access the system. Obviously this type of information should be transmitted using an RNTI known by all terminals in the cell. Another example of “multicast” information is paging, which uses the paging channel, the PCH, in which so called paging groups are defined, with each paging group having a common group paging RNTI assigned. A third example of downlink multicast information is the so called random access response, which uses a random access RNTI. In this case as well, multiple terminals can be addressed by a group RNTI.
Thus, as explained above, a user terminal is required to simultaneously be able to receive unicast data, addressed by the terminal-specific C-RNTI, as well as common data such as system information, addressed by a different and common (non-terminal-specific) RNTI. When several terminals are addressed simultaneously, as a group, they should not transmit any ACK/NACK on the PUCCH, since the network may not be able to tell from which terminal each of the ACK/NACKs originated. For this reason, in the LTE system, the current specification states that no ACK/NACK response should be sent in such a situation. Since no ACK/NACK is transmitted, there is no need for the terminals to adjust the PUCCH transmission power in such a situation.